There are various methods for separating a component contained in a fluid, e.g., a liquid or a gas. For example, with respect to the technique to remove ionic substances contained in seawater, brackish water, etc., a separation method by a separation membrane element is increasingly utilized as a process for energy saving and resource saving in recent years. The separation membranes for use in the separation method by a separation membrane element are classified, by the pore size and separating function, into a microfiltration membrane, an ultrafiltration membrane, a nanofiltration membrane, a reverse osmosis membrane, a forward osmosis membrane, etc., and these membranes are used, for example, for the production of drinkable water from seawater, brackish water, harmful substance-containing water, etc., for the production of industrial ultrapure water, for the wastewater treatment, or for the recovery of a valuable substance.
In the membrane separation element, a raw fluid is fed to one surface of the separation membrane and a permeated fluid is obtained through the other surface. By bundling a large number of separation membranes and incorporating the bundle into a separation membrane element, the membrane area per separation membrane element can be increased and therefore, the amount of a permeated fluid produced per separation membrane element can be increased. As the separation membrane element, various forms such as spiral type, hollow fiber type, plate-and-frame type, rotating flat-membrane type and flat-membrane integration type have been proposed so far.
For example, a fluid separation membrane element used for reverse osmosis filtration involves a feed-side channel material for feeding a raw fluid to a separation membrane surface, a separation membrane for separating a component contained in the raw fluid, and a permeate-side channel material for guiding, to the central tube, a permeated fluid passed through the separation membrane and separated from the feed fluid. A polymer-made net, etc. is used as the feed-side channel material, and a knit member called a tricot having a narrower interval than that of the feed-side channel material is used as the permeate-side channel material for the purpose of preventing sinking of the separation membrane and forming a permeate-side flow path. A separation membrane is overlapped with and bonded to both surfaces of the permeate-side channel material, whereby an envelope-shaped membrane is formed. The inside of the envelope-shaped membrane forms a flow path for a permeated fluid. The envelope-shaped membrane is stacked alternately with the feed-side channel material and after adhering a predetermined portion on the opening side to the peripheral surface of a water collecting pipe, wound spirally around the pipe.
In order to offer a high-performance separation membrane element, it has been proposed to increase the loading efficiency of the separation membrane. For example, in JP-A-10-230140, a feed-side channel material having a thickness of 0.1 to 0.5 mm has been proposed. In addition, in JP-A-2000-237554, a raw water channel material partially having a large thickness has been proposed.
Furthermore, it has been proposed to increase the amount of permeate produced with the separation membrane element by decreasing the flow resistance on the permeated side. In JP-A-2006-247453, a rugged sheet-like material has been proposed as the permeate-side channel material. In WO2011/152484, a non-continuous permeate-side channel material is arranged on the back surface side of the membrane.